The University of Arizona

College of Agriculture and Life Sciences

Annual McGinnies Lecture: Plant Invasions Affect Demography and Distributions of Breeding Birds in Semiarid Grasslands

Tuesday, March 13, 2018

Speaker: Erik Anderson, 2017 Mcginnies Scholar
Time: 12:00-1:00pm
Location: ENR2, S215
Abstract: Arid and semiarid grasslands, which comprise a significant portion of the global grassland biome, are imperiled from an array of anthropogenic impacts that have altered composition of plant communities.  Encroachment by woody plants and invasions by nonnative grasses have reduced habitat for many grassland-associated species, including grassland birds, which have declined more rapidly than any other group of birds across North America.  We established 140 plots that spanned gradients in cover of woody plants and nonnative grasses in grasslands of southeastern Arizona and evaluated how these plant invasions affected species richness, density, habitat selection, and nesting success of breeding birds.  Encroachment by woody plants influenced breeding birds strongly, with distributions and densities of most grassland-obligate species decreasing sharply as woody cover increased.  As encroachment progressed, overall density of birds increased as shrub-associated species were recruited.  Species richness increased with encroachment, plateauing when woody cover reached ~25%, where losses of grassland-associated species surpassed gains in shrub-associated species.  Effects of invasions by nonnative grasses on density and nest success of grassland obligates were mixed.  For some bird species, nonnative grasses decoupled the cues they used to select breeding habitat from the resources associated with those cues over evolutionary time.  For these species, areas invaded by nonnative grasses might function as ecological traps by attracting individuals away from areas of high-quality habitat into areas where reproductive success is lower.  Understanding how plant invasions affect native birds in grasslands can benefit conservation and restoration efforts by identifying achievable targets for control of nonnative grasses and shrubs that threaten imperiled grassland species